This invention concerns a device for optical chopping of a laser beam into discrete light pulses incident sequentially and repeatedly on a number of target points.
With the use of lasers for the treatment or machining of substrates, the problem of a simultaneous or nearly simultaneous incidence on the substrate in several target zones often arises. The application of several lasers as a rule is impossible for reasons of cost and space. A division of the beam by a so-called beam splitter is unfavorable because the resulting partial beams have a correspondingly diminished intensity which is not sufficient for certain machining processes and the split beams furthermore exhibit changing and in any case different intensities.
If laser beams are used, e.g. for the perforation of paper, a certain, relatively high and constant intensity of the laser beam performing the perforation must be assured in order to obtain a uniform size and quality of the perforations. In that case, beam splitting would be unfavorable for the reasons mentioned above.
A device for optical chopping of a laser beam is already known in which a continuous laser beam is introduced into an optical mirror system consisting of several consecutive rotating disks exhibiting reflecting and transmitting segments. The system thus generates a large number of light paths formed by the different combination of reflecting and transmitting segments. The beam introduced into the system is guided into the different light paths in steps according to the respective angular position of the disks and in this process, the beam is successively incident on different target points. Such an arrangement makes it possible to provide a paper web passing through the system at high speed with rows of perforations located transverse to the machine direction. The known device has several disadvantages, however. Since only a limited number of perforation combinations find space on the disks, it is not possible to realize an arbitrarily high perforation frequency. Since the beam paths have different lengths, this gives rise to focusing difficulties on the substrate.
This invention provides improved apparatus of the type described above which will furnish the highest chopping frequency, but at the same time is simple in structure and contains only a minimum of moving parts.